JP4022207B2 - Lithographic apparatus and device manufacturing method - Google Patents

Description

  The present invention relates to a radiation system for supplying a projection beam of radiation; a support structure for supporting patterning means useful for patterning the projection beam according to a desired pattern; a substrate holder for holding a substrate A holder comprising means for providing a holding force for pressing the substrate; a releasing means for applying a releasing force to release the substrate from the substrate holder against the holding force; and the patterning To a lithographic projection apparatus comprising: a projection system for projecting a focused beam onto a target portion of the substrate.

As used herein, the term “patterning means” should be broadly interpreted to refer to a means that can be used to give an incident radiation beam a patterned cross-section corresponding to the pattern to be created on the target portion of the substrate. The term “light valve” can also be used in this context. In general, the pattern will correspond to a particular functional layer in a device being created in this target portion, such as an integrated circuit or other device (see below). Examples of such patterning means include the following:
– Mask. The concept of a mask is well known in lithography and includes mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. When such a mask is placed in the radiation beam, selective transmission (in the case of a transmissive mask) or selective reflection (in the case of a reflective mask) of radiation incident on the mask occurs according to the pattern on the mask. In the case of a mask, the support structure is typically a mask table that can hold the mask in a desired position in the incident radiation beam and that it can be moved relative to the beam if desired. Guarantees;

-Programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is (for example) that the addressed area of this reflective surface reflects incident light as diffracted light, while the non-addressed area reflects incident light as undiffracted light. It is. Using a suitable filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this way, the beam is patterned according to the addressing pattern of the matrix addressable surface Will come to be. An alternative embodiment of a programmable mirror array uses a matrix arrangement of micromirrors, each of which is individually tilted about an axis by applying an appropriate local electric field or by using piezoelectric actuation means Can do. Again, these mirrors are matrix addressable, and the addressed mirrors reflect the incident radiation beam in a different direction than the unaddressed mirrors; in this way, the reflected beam is addressed by the addressing pattern of these matrix addressable mirrors. Pattern according to Necessary addressing can be done using suitable electronic means. In both cases described above, the patterning means can include one or more programmable mirror arrays. Further information on mirror arrays such as those referred to herein can be found in, for example, US Pat. Nos. 5,296,891 and 5,523,193, and International Patent Publication Nos. WO98 / 38597 and They can be gathered from WO 98/33096, which are incorporated herein by reference. In the case of a programmable mirror array, the support structure may be embodied as a frame or table, for example, which may be fixed or movable as required; and-a programmable LCD array. An example of such a configuration is given in US Pat. No. 5,229,872, which is hereby incorporated by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.

  For simplicity, the rest of this text may be specifically directed at some places with examples with masks and mask tables; however, the general principles discussed in such cases are given above Such a patterning means should be viewed in a broad context.

  Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning means may create circuit patterns corresponding to the individual layers of the IC, and the target of the substrate (silicon wafer) coated with a layer of radiation sensitive material (resist). An image can be formed on a portion (eg, including one or more dies). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. Current devices that use patterning with a mask on a mask table can distinguish between two different types of machines. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once; such an apparatus is commonly referred to as a wafer stepper or step-and-repeat apparatus. In an alternative device—usually called a step-and-scan device—the target pattern is irradiated by sequentially scanning the mask pattern in a given reference direction (“scan” direction) under the projection beam, while in general Since the projection system has a magnification M (generally <1) and the speed V at which the substrate table is scanned is the speed at which the mask table is multiplied by the magnification M, the substrate table can be parallel or reversed in this direction. Scan in parallel with each other. Further information regarding lithographic apparatus as described herein can be gathered, for example, from US Pat. No. 6,046,792, which is hereby incorporated by reference.

  In a manufacturing process using a lithographic projection apparatus, a pattern (eg in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may be subjected to various processes such as, for example, priming, resist coating and soft baking. After exposure, the substrate may undergo other processing such as post exposure bake (PEB), development, hard bake and imaging morphology measurement / inspection. This series of processes is used as a basis for patterning individual layers of a device, eg, an IC. The layer thus patterned is then subjected to various processes intended to finish individual layers, such as etching, ion implantation (doping), metallization, oxidation, chemical and mechanical polishing, etc. You may receive it. If several layers are needed, the entire process or variations thereof would have to be repeated for each new layer. Eventually, an array of devices can be formed on the substrate (wafer). These devices can then be separated from each other by techniques such as dicing or sawing, from which the individual devices can be attached to a carrier, connected to pins, and the like. More information on such a process can be found, for example, by Peter Van Zandt, “Microchip Fabrication: A Practical Guide to Semiconductor Processing”, 3rd edition, McGraw Hill Publishing Company, 1997, ISBN0-07-067250-4 It can be obtained from the book, which is incorporated herein by reference.

  For simplicity, this projection system may hereinafter be referred to as a “lens”; however, the term may refer to various types, including refractive optical elements, reflective optical elements, and catadioptric optical elements, for example. It should be interpreted broadly to encompass projection systems. The radiation system may also include components that act according to any of these design types to direct, shape, or control the projection beam of radiation, and such components are also collectively or singularly “lenses” below. You might call it. Furthermore, the lithographic apparatus may be of a type having two or more substrate tables (and / or two or more mask tables). In such “multi-stage” devices, additional tables may be used in parallel, or the preparatory process may be performed on one or more tables, while one or more other tables may be used for exposure. A two-stage lithographic apparatus is described, for example, in US Pat. No. 5,969,441 and International Patent Publication No. WO 98/40791, both of which are incorporated herein by reference.

  Although this text may specifically refer to the use of the device according to the invention in the manufacture of ICs, it should be clearly understood that such a device has many other possible uses. is there. For example, it may be used for manufacturing integrated optical systems, inductive detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, and the like. Those skilled in the art will recognize that any of the terms “reticle”, “wafer”, or “die” used herein in this context are the more general terms “mask”, “substrate”, and “ You will see that it should be considered to be replaced by the “target part”.

  In this document, the terms “radiation” and “beam” are used to refer to ultraviolet (UV) radiation (eg, wavelengths 365, 248, 193, 157 or 126 nm) and extreme ultraviolet (EUV) radiation (eg, in the range of 5-20 nm). ), As well as all types of electromagnetic radiation including particle beams, such as ion beams or electron beams.

  In a conventional lithographic projection apparatus, during the photolithography process, the wafer is firmly clamped on the wafer holder by holding forces that may range from vacuum pressure to electrostatic forces, intermolecular bonding forces or gravity. The wafer holder forms a substantially flat plane, usually in the form of a plurality of protrusions that form a flat plane that clamps the wafer thereon. Small variations in the height of these protrusions are detrimental to image resolution because small deflections from the ideal flat surface configuration of the wafer can cause wafer rotation and this rotation may cause overlay errors. . Moreover, such height variation of the wafer holder may cause height variation of the wafer supported thereby. During this photolithography process, such height variations may affect image resolution due to the limited focal length of the projection system. Therefore, it is very important to obtain an ideally flat wafer holder.

  It has become apparent to the inventors that this clamping force may cause problems when releasing the wafer from the wafer holder.

  Conventional ejection mechanisms raise the release force to some degree to a substantially high level, thereby biasing the wafer to an initial bias shape, where the wafer is released from the wafer holder by converting this bias energy into a release action. It is configured to wait until For example, when using vacuum pressure as the clamping force, the wafer is initially bent so that it is substantially released from the wafer holder at the center of the wafer. The wafer is then released from the wafer holder by converting this bending energy into a release action, while when the wafer is released from the wafer holder, the vacuum pressure is reduced to substantially ambient pressure.

  Typically, to provide such release force, a tripod of three ejector pins (e-pins) is used that engages the wafer at three spaced positions and is released to detach the wafer from the wafer holder. Bring power. The energy accumulated in the wafer during the increase of the release force is converted into a displacement by releasing the wafer surface from the wafer holder surface. However, this stored energy may also cause damage to the wafer and / or wafer holder.

  The present invention addresses this problem and aims to overcome this problem by providing a photolithographic machine in which the amount of remaining energy is not detrimental to the wafer and / or wafer holder when the wafer is finally released from the wafer holder. .

  This object is achieved by a lithographic projection apparatus according to the preamble, which includes a control device for applying a weakened release force just before the final release.

In this way, the release force is weakened by the control device just before the final release, so that the amount of energy that may damage the wafer and / or wafer holder, in particular the energy acting on the holding area for holding the wafer in a flat position. The amount is reduced after releasing the wafer from the wafer holder in a sudden motion and after release, compared to a constant release force that weakens rather than weakens the release force prior to the moment of final release.
The reduction in release force during release reduces the amount of energy absorbed by the wafer so that this energy does not damage the wafer and / or wafer holder during the release.

  The release force is preferably controlled to be less than 70% of the maximum release force at the final release. More preferably, the release force is controlled in proportion to the preset release height of the release means. In particular, the difference between the actual wafer height near the e-pin and the preset release height is measured. The actual height of this wafer during release depends on the release force that determines the maximum angle of rotation of the wafer and that is applied to the wafer during final release, particularly near the final release area where the substrate is finally released from the wafer holder. By keeping this angle of rotation small, the maximum amount of energy to be transferred to the wafer holder is low, thereby keeping this amount of energy below a threshold that can be absorbed to the maximum, thus leaving the wafer and / or wafer holder intact. Keep it.

  In a preferred embodiment, the release force is selected to be a maximum deflection angle of 2 mrad. Here, the predetermined release height with respect to the 200 mm substrate is less than 1.0 mm, preferably less than 0.5 mm. In order to absorb the surplus energy still remaining during final release from the wafer holder of the wafer, the wafer holder preferably includes a protective rim for absorbing wear energy. In this way, this energy is absorbed in areas where the flatness of the wafer holder is not important. Therefore, the flatness can be maintained by this photolithography process.

  The invention further provides a device manufacturing method comprising: providing a substrate at least partially covered with a layer of radiation sensitive material; providing a holding force for pressing the substrate into a substrate holder; Providing a projection beam of radiation using a radiation system; using a patterning means to pattern the cross section of the projection beam; applying the patterned beam of radiation onto a target portion of the layer of radiation sensitive material; And applying a release force to release the substrate from the substrate holder against the holding force. According to the invention, the method includes the step of controlling the release means to apply a weakened release force just prior to final release.

  Preferably, the release force and / or the release height is determined in a repetitive manner during processing. In this way, the magnitude of the release force to be applied to the wafer can be easily and quickly found in a high throughput photolithography process without causing unnecessary damage to the wafer holder.

  More preferably, the release force and / or the release height is determined based on the release force and / or release height recently applied during processing. Statistical averaging of such recent results, eg, the last 10 results, will provide a heuristic value while keeping damage to the wafer to a minimum.

  In a further aspect, the invention relates to a lithographic projection apparatus according to the preamble, wherein the substrate holder comprises a protective rim for absorbing wear energy. Such a protective rim absorbs excess release energy remaining after release of the substrate from the substrate holder while keeping the substrate holder itself intact.

  In yet a further aspect, the invention is a device manufacturing method comprising: providing a substrate at least partially covered with a layer of radiation sensitive material; holding force for pressing the substrate into a substrate holder Providing a projection beam of radiation using a radiation system; using patterning means to pattern the cross-section of the projection beam; applying the patterned beam of radiation to the radiation-sensitive material; Projecting onto the target portion of the layer; applying a release force to release the substrate from the substrate holder against the holding force; and repeating the release force and / or release height during processing. The present invention relates to a method including a step determined by the method.

  Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference symbols indicate corresponding parts, and in which:

FIG. 1 schematically depicts a lithographic projection apparatus according to a particular embodiment of the invention. This device:
A radiation system Ex, IL, which also includes a radiation source LA in this special case for supplying a projection beam PB of radiation (for example light in the far ultraviolet region);
A first object table (mask table) MT comprising a mask holder for holding a mask MA (eg a reticle) and coupled to the first positioning means PM for accurately positioning the mask with respect to the member PL;
A second object table comprising a substrate holder for holding the substrate W (for example a silicon wafer coated with resist) and coupled to the second positioning means PW for accurately positioning the substrate with respect to the member PL (Substrate table) WT; and-a projection system ("lens") PL for imaging the irradiated portion of the mask MA onto a target portion C (e.g. including one or more dies) of the substrate W.

  As depicted here, the device is transmissive (ie has a transmissive mask). In general, however, it may be, for example, reflective (with a reflective mask). Alternatively, the apparatus may use other types of patterning means, such as a programmable mirror array of the type mentioned above.

  This source LA (eg, an excimer laser source) produces a beam of radiation. This beam is sent directly or through a conditioning means such as a beam expander Ex and then into the illumination system (illuminator) IL. The illuminator IL may include adjusting means AM for setting the outer and / or inner radial extent (commonly referred to as σ outer and / or σ inner, respectively) of the intensity distribution of the beam. In addition, it typically includes various other components such as an integrator IN and a capacitor CO. In this way, the beam PB incident on the mask MA has a desired uniformity and intensity distribution in its cross section.

  With reference to FIG. 1, the source LA may be within the housing of the lithographic projection apparatus (as is often the case when the source LA is, for example, a mercury lamp) but is remote from the lithographic projection apparatus. Note that the beam of radiation it creates may be directed to this device (eg, using a suitable directing mirror); this latter scenario is often the case when the source LA is a laser. That is. The present invention and claims encompass both of these scenarios.

  The beam PB then traverses the mask MA held on the mask table MT. After traversing the mask MA, the beam PB passes through the lens PL, which focuses this beam PB onto the target portion C of the substrate W. Using the second positioning means PW (and the interferometer measuring means IF), the substrate table WT can be moved precisely, for example so as to place different target portions C in the path of the beam PB. Similarly, the first positioning means PM can be used to accurately position the mask MA with respect to the path of the beam PB, for example after mechanical retrieval of the mask MA from a mask library or during a scan. In general, the movement of the object tables MT, WT is realized using a long stroke module (coarse positioning) and a short stroke module (fine positioning), which are not clearly shown in FIG. However, in the case of a wafer stepper (unlike a step-and-scan apparatus), the mask table MT may only be coupled to a short stroke actuator or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

The illustrated device can be used in two different modes:
1. In step mode, the mask table MT is held essentially fixed, and the entire mask image is projected onto the target portion C at once (ie, with a single “flash”). The substrate table WT is then moved in the x and / or y direction so that a different target portion C can be irradiated with the beam PB; In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed with a single “flash”. Instead, the mask table MT can move at a velocity v in a given direction (so-called “scan direction”, eg, y direction), so that the projection beam PB is scanned over the mask image; The WT is moved with it at the speed V = Mv in the same or opposite direction, where M is the magnification of the lens PL (typically M = 1/4 or 1/5). In this way, a relatively large target portion C can be exposed without having to compromise on resolution.

  FIG. 2 shows an initial stage in which the wafer 1 is released from the wafer holder 2. The wafer holder 2 includes support pins (eg, cylindrical burl, not shown) having a height of about 100 μm. These bars are spaced from each other by a distance of about 3 mm. These bars are about 0.5 mm in diameter. Each protrusion is embodied (sized) such that the tip is remote from the surface of the substrate holder so that the tips are all in a single substantially flat surface. The wafer holder 2 may be supported on the flat support 3.

  The wafer 1 is normally released from the holder 2 by three (only two of which are shown) discharge pins 4, and these pins are controlled by a control device 5 that controls the displacement of the discharge pins 4. Such a control device 5 may be, for example, a software routine that controls the function of the electric motor 6 that drives the discharge pin 4. Moreover, the control device 5 may be implemented in a hardware device, for example in a design using pre-configured digital and / or analog hardware devices that react to certain detection inputs 7 of the discharge system 8. The shape of the wafer 1 in FIG. 2 is bell-shaped, that is, at this stage, it can be considered that only the central area near the discharge pins is released. The discharge pins provide a release force to the wafer and result in biasing the wafer 1 to accumulate energy when the wafer is bent. The wafer 1 is released from the substrate holder in the central region, while the outer region of the wafer 1 is still clamped to the substrate holder due to vacuum suction.

  FIG. 3 shows a schematic view of the substrate 1 in the final stage of release. At this stage, the wafer has a “bowl” shape, ie, almost all of the wafer 1 has been released and only the outer area of the wafer and the wafer holder are in contact. At this stage, the shape of the wafer is substantially convex so that the wafer surface is slightly rotated with respect to the wafer holder, as will be described in detail with reference to FIG. Such rotation may introduce mechanical friction, potentially causing damage. The outer region of the example of FIG. 3 consists only of a few rings of concentric protrusions or a sealing ring for creating a vacuum. Final release occurs when the wafer is rotated away from this outermost peripheral region of the wafer holder.

  FIG. 4 shows a detailed view of the wafer 1 close to the outermost peripheral area of the wafer holder 2 being released. In this example, the wafer holder 2 includes a series of burl rings, showing the second burl ring 9 and the last burl ring 10 from the last. Further, the wafer holder 2 includes a sealing rim 11. This rim 11 is dimensioned to form a “leak” seal, ie, due to the small difference in height between the rim 11 and the burls 9 and 10, air enters the space created between these burls. In this way, a holding force that spreads from the center of the wafer to the sealing rim is generated, so that the substrate 1 is pressed substantially flat against the substrate holder 2. When the last burl ring 9 no longer contacts the wafer 1 and the wafer 1 rotates, the wafer 1 will rub against the contact point 12. This rubbing is caused by the fact that the center line of the wafer rotates and that the bottom surface is forcibly moved toward the center of the wafer holder 2 as indicated by the arrow P. This rubbing distance is half the thickness of the wafer on which the wafer is rotated. The energy associated with this rubbing effect can be calculated as the product of force and distance. This force is a frictional force proportional to the normal force generated between the wafer 1 and the wafer holder 2 and will be maximum where the wafer rotation is maximum and therefore near the wafer holder boundary. Depending on the design of the wafer holder 2, the last contact point may be the last burl ring 10, the outer rim 11 or even a further rim element 13, which absorbs this rubbing energy associated with the release action. May be used to

  FIG. 5 depicts a power diagram of wafer ejection from a conventional wafer holder. In this figure, three simultaneous events are depicted: the top line 14 shows the force applied to the substrate by the discharge pins; the middle line 15 is a preset control of the wafer height in response to the application of the release force. A dotted line immediately below the intermediate line 15 indicates the actual height of the wafer 1 in response to the application of the release force. The lower line 16 depicts the drop in vacuum pressure (ie, the pressure difference from ambient pressure), which drops to zero immediately after full release of the wafer. In the diagram of FIG. 5 it becomes clear that after the wafer has been completely released, the release force drops to a level sufficient to support the wafer 1. From the point of view of the discussion of energy converted to rub energy with reference to FIG. 4, the area under the force line 14 up to the release instant 17 in FIG. 5 corresponds to the energy converted to release action; Obviously, the area under the force line 14 after the moment 17 is proportional to the rubbing action and the energy absorption near the boundary of the wafer holder 2; it may damage the wafer 1 and / or the wafer holder 2. Thus, this release moment 17 may be regarded as the moment when the outer region of the wafer, in particular, the penultimate burl ring 9 starts to release from the wafer holder 2. From this release instant 17, the edge of the wafer rotates around the wafer holder 2, in particular around the rim 11. It should be noted that the area under the force line 14 after the release moment 17 should be minimized as much as possible, and therefore the substrate 1 should be released from the holder 2 with a weakened release force just before the final release. This is a table.

  FIG. 6 is an explanatory diagram showing a force line 14 'according to the present invention. This line of force is lowered before release, thus keeping the destructive energy generated thereby to a minimum after release. This reduction is preferably controlled to a maximum downward steep slope 18 so that maximum force is applied while releasing the wafer, thereby shortening the wafer release time. This ideally results in a force characteristic with a substantially block shape: Initially, the force rises to the height of the clipping edge 19 to provide maximum thrust, thereby releasing the wafer as fast as possible. This wafer height is preset to a predetermined set point 15, which determines to release the wafer when the set point height is reached. The actual wafer height near the discharge pin is entered into the controller 5, which should be added to the preset release height of the discharge pin based on the differential analysis between the set point height and the actual height. Decide the release force. This differential analysis may include terms of time integration and time differentiation of this actual difference, in addition to a term proportional to the difference between the set point and the actual height.

  FIG. 7 depicts a rough prediction of the energy generated at the final stage of the wafer release action for a 200 mm wafer with a Young's modulus of 190 GPa and a thickness of 0.7 mm. With this prediction, the applied vacuum pressure was 0.5 bar and the e-pin force applied there was 12N. In this case, it was found that when the pressure was kept at 7 mbar, the wafer was just released from the penultimate burl ring 9 while still being supported by the last burl ring 10 and thus creating a stable state. . Between 7 and 3.5 mbar, the wafer will rotate around the outer support point. At 3.5 mbar, the vacuum pressure will have to be lowered to keep the wafer pressed against the last bar. The wafer will then move away from the table and the e-pin force will be equal to the wafer weight. In order to find a quantitative measure of wear energy, the following information is needed: normal contact force; slip force from friction coefficient and normal contact force; and slip distance from wear rotation.

  It was found that for an applied e-pin force of 12 N, the wafer edge contact force on the last burl ring was still 12 N at the beginning of the bowl-shaped portion of the process. The wafer rotation at the end of this bowl shape was found to be 5 mrad. Here, it is assumed that the friction coefficient is 0.2. FIG. 7 shows the relationship between contact force and wafer rotation: the contact force drops from 12N to zero while the wafer is rotating to 5 mrad. At 1 mm outside the last burl ring, the wafer will bend over 5 μm for 5 mrad rotation. With a 3 μm vacuum seal under these bars, this vacuum seal will be the contact point in 60% of the rotation process. It will be appreciated that changes in the height of the outer rim affect the amount of energy transferred to the outer burl ring 10 or the sealing rim 11. Therefore, in the example in which the sealing rim 11 is 3 μm below the outer burl ring 10, the outer burl ring 10 consumes 60% of the friction energy and the sealing rim 11 consumes 40%.

Routine for calculating friction energy for a 6Ne pin scenario where the amount of energy consumed by the outer rim 11 is zero, while the energy absorbed by the outer burl ring 10 is only 25% of the energy generated by 12N. In fact, it has been found that this energy is quadratic with respect to the applied force. A series of adaptations were calculated, where parameters such as, among other things, the height of the outer rim, the presence or absence of the protective rim element 13 and the applied force were varied.
The results are summarized in the following table:

  From this table, it is necessary to release the substrate from the holder to the substrate holder, and more specifically to release with a weakened release force just before the final release, which acts on the holding area for holding the wafer in a flat position. It is clear that the planning process can be considered. In an actual production process, the release force and / or the release height may be determined iteratively during processing. In this way, the magnitude of the release force to be applied to the wafer can be easily and quickly found in a high throughput photolithography process without causing unnecessary damage to the wafer holder. Further, the release force and / or the release height may be determined based on the release force and / or release height that has recently been applied during processing. For example, in a batch process where a batch of wafers is discharged from the wafer holder in a later photolithography process, the method may include a discharge routine that discharges the wafers based on the latest average release force. Statistical averaging of such recent results, eg, the last 10 results, will provide a heuristic value while keeping damage to the wafer to a minimum. In this way, exceptionally only, for example, a pre-set maximum release force, e.g. a preset maximum, to release a wafer clamped with a clamp force exceeding the average on the wafer holder due to sticking or other non-average conditions The release force will have to be applied in a later iteration.

  In this way, the average excess frictional energy applied during wafer release can be reduced for batch processing, thereby significantly reducing wear on the substrate holder.

  While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. This description is not intended to limit the invention.

1 shows a lithographic projection apparatus according to an embodiment of the invention. The initial stage of the release of the wafer from the wafer holder is shown. 2 shows the final stage of wafer release from the wafer holder. FIG. 4 shows a detailed view of the wafer and wafer holder at the final stage of release. FIG. 6 shows a power diagram for discharging a wafer from a conventional wafer holder. FIG. 6 is a modified force diagram showing wafer discharge control according to the present invention. It is explanatory drawing of the energy which the wafer holder absorbed in the final stage of release.

Explanation of symbols

5 Control Device 11 Protective Rim C Target Part Ex Beam Expander IL Illumination System LA Radiation Source MA Patterning Means MT Support Structure PB Projection Beam PL Projection System W Substrate

Claims (8)

A radiation system for supplying a projection beam of radiation,
A support structure for supporting a patterning means which serves to pattern this projection beam according to a desired pattern;
A substrate holder for holding a substrate, a holder having means for giving a holding force for pressing the substrate,
Release means for applying a release force to release the substrate from the substrate holder against the holding force;
A lithographic projection apparatus comprising: a projection system for projecting the patterned beam onto a target portion of the substrate; and a controller for applying a weakened release force immediately before final release ,
The controller is configured to control the release force such that the release force is less than 70% of a maximum release force in a final release;
The control device is configured to control the release force in proportion to a preset release height of the release means.
Lithographic projection apparatus. A lithographic projection apparatus according to claim 1 , wherein the release force is selected to be a maximum deflection angle of 2 mrad. A lithographic projection apparatus according to claim 1 or 2 , wherein the predetermined open height for a 200 mm substrate is less than 1.0 mm, preferably less than 0.5 mm. The lithographic projection apparatus according to any one of claims 1 to 3, wherein the substrate holder includes a protective rim for absorbing wear energy. 5. The substrate holder according to any one of claims 1 to 4, wherein the substrate holder includes a plurality of protrusions, the tips of which form a substantially flat support plane for supporting a substantially flat substrate. Lithographic projection apparatus. Providing a substrate at least partially covered with a layer of radiation sensitive material;
Preparing a holding force for pressing the substrate into the substrate holder;
Preparing a projection beam of radiation using a radiation system;
Using patterning means to pattern the cross section of the projection beam;
Projecting the patterned beam of radiation onto a target portion of the layer of radiation sensitive material;
Step applying a release force to release from said substrate holder against the substrate to the holding force, and such that the release force just before the final releasing is weakened, including the step of controlling the application of said release force A device manufacturing method comprising:
A device manufacturing method further comprising the step of controlling the application of the release force in proportion to a preset release height of a release means used to apply the release force. The device manufacturing method according to claim 6 , wherein the release force and / or the release height is determined in a repetitive manner during processing. The device manufacturing method according to claim 6 or 7 , wherein the release force and / or the release height is determined based on a release force and / or a release height applied during a recent process.

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